The present invention relates to improved replica routing techniques and dynamic server organization.
In a dynamic server organization system, server requests are originated by client computers (clients). Programs such as browsers on these client computers originate service requests, using the HTTP protocol, in response to end user actions. These service requests are sent to network servers. For example, www.nasdaq.com is an example of such a network server on the Internet. In the system described herein, certain of the network servers are routers. Many types of devices can participate in the system we describe, including network appliances. We will use the terms client computer or browser to refer to any type of system that originates service requests.
Routers serve two functions. The first function of a router is to redirect service requests to other routers that are more suitable to service the request than the router that received the request. The second function of a router is to directly service requests by interpreting and performing the actions contained in the request. We will say that a router services a request when it directly performs a request and returns the result to the computer that sent the service request message. We will say that a router routes a request when it redirects a request to another router for processing. The entire process of deciding which router will service a request is called request routing.
In a hierarchy of routers, request routing can be performed in a restrictive or open manner. Restrictive request routing limits the routers that service a request, in order to optimize network performance. For example, a router may be required to be on the same local area network as the client computer in order to be permitted to service requests from the client. If all routers are operating, a restrictive policy can be used to optimize a desired performance metric. If not all routers are functioning, however, a restrictive policy can reduce the probability that a request can be serviced. Open routing is less restrictive and permits more routers to service a request. For example, any router that is within two network hops of a client may be permitted to service a request. While open routing increases the chances that a request can be serviced, it may not optimize a desired performance metric. One of the contributions of the present invention is a mechanism for combining the best elements of restrictive and open policies for request routing.
U.S. patent application Ser. No. 08/779,770, filed Jan. 7, 1997 entitled “Replica Routing,” the entire disclosure of which is hereby incorporated herein by reference, discloses replica routing techniques.
It is known to provide statically configured hierarchal network services such as network time protocol (NTP) that use a hierarchial organization to disseminate information (such as time distribution) through the hierarchy so that a root server (which in NTP is a server attached to an atomic clock) is not overloaded with requests.